In a friction drive belt, such as a raw-edged V-belt or V-ribbed belt, in which a compression rubber layer forming a contact part of a belt body with a pulley is made of a rubber composition, it is a generally known technique to blend carbon black into the rubber composition used for the compression rubber layer.
For example, PATENT DOCUMENT 1 shows that a compression rubber layer of a V-ribbed belt is made of a rubber composition containing (A) 20-60 parts by weight of carbon black having a specific surface area, measured by nitrogen adsorption, of equal to or greater than 70 m2/g and a dibutyl phthalate absorption of less than 100 cm3/100 g, and (B) 15-55 parts by weight of carbon black having a specific surface area, measured by nitrogen adsorption, of less than 70 m2/g and a dibutyl phthalate absorption of less than 100 cm3/100 g per 100 parts by weight of rubber. The document describes that this composition of the compression rubber layer can improve the wear resistance, endurance, and quieter performance thereof.
PATENT DOCUMENT 2 shows that a compression rubber layer of a drive belt is made of an ethylene/α-olefin copolymer rubber composition which contains 50 or more parts by weight of carbon black per 100 parts by weight of rubber and in which the carbon black includes 30 or more parts by weight of large particle carbon black having an iodine absorption of equal to or less than 40 mg/g per 100 parts by weight of rubber. The document describes that this composition prevents the life of the drive belt from being shortened and allows the improved advantage of noise reduction to continue for a long time.
Furthermore, in a friction drive belt, it is also a generally known technique to blend short fibers into a rubber composition used for a compression rubber layer.
For example, PATENT DOCUMENT 3 shows that the amount of reinforcing short fibers blended into a compression rubber layer of a drive belt is 15-30 parts by mass per 100 parts by mass of rubber, and the amount of short vinylon fibers blended into the compression rubber layer is 1-4 times greater than that of nylon fibers blended thereinto. The document describes that the above amounts of blended fibers can improve the dynamic fatigue life of the drive belt and further stabilize the friction coefficient thereof without reducing the processability of rubber.
PATENT DOCUMENT 4 shows that short nylon fibers, short vinylon fibers, and other fibers are blended into a compression rubber layer of a V-ribbed belt and the short fibers are arranged to protrude beyond the surface of the belt and increase in cross-sectional area. The document describes that this arrangement can prevent abnormal noise due to stick-slip phenomena.
PATENT DOCUMENT 5 shows that short aramid fibers and short non-aramid fibers are both blended into a compression rubber layer of a V-ribbed belt, and that some of only the short aramid fibers protrude beyond the surface of the belt while some of the short non-aramid fibers are exposed at the surface of the belt in order to prevent the protruding short aramid fibers from being embedded in the belt. The document describes that this can solve completely different problems, i.e., belt wear and slip caused due to an increase in the time during which the belt runs.
PATENT DOCUMENT 6 shows that soluble short fibers are blended into a compression rubber layer of a V-ribbed belt. This can reduce the belt slip ratio and attenuate noises during the belt run.
PATENT DOCUMENT 7 shows that short fibers of gellable polyvinyl alcohol subjected to an RFL treatment are blended into a compression rubber layer of a V-ribbed belt. The document describes that this can effectively prevent a reduction in the drive capability of the drive belt and abnormal noise both arising from slips of the drive belt upon exposure thereof to water.    PATENT DOCUMENT 1: Japanese Patent Publication No. 2006-183805    PATENT DOCUMENT 2: Japanese Patent Publication No. 2006-316812    PATENT DOCUMENT 3: Japanese Patent Publication No. H10-213184    PATENT DOCUMENT 4: Japanese Patent Publication No. H03-219147    PATENT DOCUMENT 5: Japanese Patent Publication No. H07-004470    PATENT DOCUMENT 6: Japanese Patent Publication No. 2003-314624    PATENT DOCUMENT 7: Japanese Patent Publication No. 2006-118661